Alginate, the salt of alginic acid, is a linear polysaccharide naturally produced by brown seaweeds (Phaeophyceae, mainly Laminaria). It is composed of typically 100-3000 monomer residues linked together in a flexible chain. These residues are of two types, namely β-(1→4)-linked D-mannuronic acid (M) residues and α-(1→4)-linked L-guluronic acid (G) residues, respectively. The residues are epimers (D-mannuronic acid residues being enzymatically converted to L-guluronic acid residues after polymerization) and only differ at C5. However, in the polymer chain they give rise to very different conformations; any two D-mannuronic acid residues are 4C1-diequatorially linked while the link connecting any two L-guluronic acid residues is a 1C4-diaxial link, as illustrated in Formula I, herein below.

The residues are organised in blocks of identical or strictly alternating residues (e.g. MMMMMM . . . GGGGGG . . . or GMGMGMGM . . . ).
Different monovalent and polyvalent cations, e.g. Na+, K+, NH4+, Mg2+ and Ca2+, are present as counter-ions to the negatively charged groups of the alginates.
Depending on factors such as mean polymer chain length, polymer composition and the cations present the flow characteristics of alginates vary widely, from free-flowing (low viscosity) to drip-free (high viscosity).
Alginates find uses in various fields, e.g. in pharmaceutical and food products where they are applied e.g. as thickeners, stabilizers and gelling agents. Their use in pharmaceutical compositions is mentioned in a number of patents and patent applications. Thus, U.S. Pat. No. 6,923,988 assigned to Lipocine, Inc. discloses a solid pharmaceutical composition for improved delivery of active ingredients. It is mentioned that the pharmaceutical composition may comprise alginate as a disintegrant.
U.S. Pat. No. 6,923,981 assigned to Warner-Lambert Company discloses fast dissolving orally consumable films for mouth hygiene. A listing of film forming agents is given and while sodium alginate is mentioned therein, pullulan is stated to be preferred and no example of an alginate film is given.
U.S. Pat. Nos. 6,656,493 and 6,740,332, both assigned to Wm. Wrigley Jr. Company disclose edible film formulations for mouth hygiene. The film formulations contain at least three types of film forming agents, viz. a maltodextrin, a hydrocolloid and a filler. The aim of the hydrocolloid is to provide thickness and decrease brittleness and alginates are mentioned as examples of a hydrocolloid.
US patent application No. 20050013847, assigned to FMC Corporation, relates to delivery systems comprising a homogenous, thermoreversible gel film, wherein the gel film comprises: a film forming amount of a water soluble thermoreversible alginate and optionally at least one of a plasticizer, a second film former, a bulking agent, and a pH controlling agent; and an active substance. The second film former is said to be optional but all examples show films comprising at least two film formers. The exemplified process for preparing the gel film comprises heating the alginate-containing mixture to an elevated temperature to form a homogeneous molten composition. The active substance is added either prior to or after formation of the molten composition and the molten composition containing the active substance then is cooled and further processed. It is mentioned that to modify the dissolution profile of the dosage forms the films can contain added components that can create solid dosage forms having immediate, enteric or delayed release capabilities.
U.S. Pat. No. 6,709,671, assigned to LTS Lohmann Therapie-Systeme AG discloses a monolayer film formed from a mucoadhesive composition which comprises at least one water-soluble polymer; a surfactant alone or in combination with at least one member selected from the group consisting of a polyalcohol and a plasticizer, or a polyalcohol and a plasticizer; and at least one cosmetic or pharmaceutical ingredient, for application into the mouth.
There are many ways of delivering active pharmaceutical ingredients (drugs) to the body (collectively termed formulations) depending on the type of drug and the disorder to be treated. For example, oral formulations such as tablets, capsules and lozenges; solutions of drugs in vials and pre-filled syringes for injection; topical formulations such as patches and ointments as well as nasal sprays. Other ways of delivering drugs, such as implanted pumps and slow-release depot formulations to be placed in the body, also exist. The formulation selected will typically have a marked influence on the therapeutic result of the drug, its side effects and the ease by which the patient can use the medication.
The most widely used drug formulation is the tablet that shall be swallowed for release of drug in the intestine. Tablets consist of a drug that is mechanically compressed together with a number of additional substances providing the structure and delivery properties of the tablet. Tablets need to be swallowed with a liquid such as water and some patients, e.g. children and elderly patients, may have difficulties in swallowing them.
A problem associated with oral tablets is that many drugs may be degraded during the passage through the acid environment of the stomach. When the drug has entered the intestine, drug is taken up into the blood stream via the portal vein into the liver where a large portion of the active pharmaceutical ingredients typically is metabolised to inactive chemicals by enzymes that normally take care of foreign substances in food, viz. the so-called first-pass metabolism.
These factors result in a significant delay before a positive therapeutic effect can be noted, leading to a risk of gastro-intestinal side effects augmented by the need of administering considerably higher amounts of drug than would be needed by, for example, a direct injection of a drug solution into a vein.
Although injections provide a rapid pharmacological effect and reduce the risk of side effects, injections usually must be carried out by medically qualified staff at a medical centre or hospital, thus limiting the convenience of this administration form.
Nasal sprays may produce a rapid onset of action but is usually limited to local treatment of the respiratory tract. Other forms of formulations such as depots, patches or infusion devices are usually applied to address conditions where a sustained level of drug is required over longer time periods.